feat: add RemoteLoadableBanner component to layout

[bmuenzenmeyer]

Adds the missing banner driven off of https://nodejs.org/site.json

This helps preserve a unified experience - even if there is a loading state

[cursor]

PR Summary

Low Risk
Single UI addition reusing an existing doc-kit banner component; no auth, data, or routing changes.

Overview
Adds the shared RemoteLoadableBanner from doc-kit at the top of the learn layout so announcement content from nodejs.org/site.json can show on learn pages, matching the main site (including a loading state while remote config loads).

The change is limited to importing the component and rendering it above analytics, nav, and article content in components/Layout/index.jsx.

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Project	Deployment	Actions	Updated (UTC)
nodejs-learn	Ready	Preview	Jul 4, 2026 2:53pm

[github-actions]

👋 Codeowner Review Request

The following codeowners have been identified for the changed files:

Team reviewers: @nodejs/nodejs-website

Please review the changes when you have a chance. Thank you! 🙏

[Copilot]

Pull request overview

Adds a remotely driven announcement banner to the site layout (per PR description: driven by https://nodejs.org/site.json), ensuring it renders across pages using the shared Layout component.

Changes:

• Import and render RemoteLoadableBanner at the top of the Layout component.

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